The purpose of this research is to develop the relations between the physical parameters of impulse noise (peak pressure, duration, number, repetition rate, etc.) and their concomitant effects on the anatomy, physiology, and hearing level of the chinchilla. Several devices will be used to create realistic impulses. Two general classes of experiments are planned: (1) parametric studies where chinchilla are initially screened either by AER or conditioning audiometry, systematically exposed to a set of impulses, and audiometric changes followed for 30 days, at which time the animal is sacrificed. (2) In-depth studies of interesting exposures where the animal will be examined by electronmicroscopy and histochemical analysis as well as traditional audiometric procedures. The emphasis for the next three-years will be on realistic exposures, therefore, chinchilla will be exposed to either "work-week" or asymptotic threshold shift regimes of impulse noise. Also, selected animals will be examined for vestibular damage. This data is necessary for the development of a scientifically based Damage Risk Criterion for impulse noise.